Disc type eccentric rotor and flat type vibrator motor having the rotor

ABSTRACT

The present invention provides a disc type eccentric rotor having at least two air-core coils, the rotor comprising a flat type commutator member having a shaft insertion through hole in the center thereof, a plurality of commutator land segments formed around the shaft insertion through hole on a first side of the flat type commutator member, wound type air-core coil arrangement guides formed around the shaft insertion through hole on a second side of the flat type commutator member, air-core coil end portion connection lands formed circumferentially on the second side of the flat type commutator member, a shaft holder installed around the shaft insertion through hole on the second side of the flat type commutator member, and wound type air-core coils installed at the wound type air-core coil arrangement guides and having the end portions thereof connected to the air-core coil end portion connection lands. The air-core coils of bigger sizes are uniformly arranged on the commutator member, so that high efficiency and easy installation can be obtained. The arrangement of the air-core coils offsets the center of gravity from the geometrical centroid of the rotor, and there is no need for an additional eccentric member. Otherwise, since the printed wiring type air-core coil is thinner than the wound type air-core coil, an eccentric weight is installed on the printed wiring type air-core coil so that a great amount of vibration may be obtained during rotation of the rotor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an improved flat type vibratormotor used as a silent call means of a mobile communications apparatusand an improved eccentric rotor which is one of the major membersthereof.

[0003] 2. Description of the Related Art

[0004] A conventional cylindrical DC motor, which is used as a silentcall means of a pager or mobile phone, is shown in FIG. 8. As shown inthe drawing, an eccentric weight W formed of tungsten alloy is installedat an output shaft S of a cylindrical DC motor M. When the motor Mrotates, vibrations are generated by the centrifugal force of theeccentric weight W.

[0005] However, this conventional method of adding the eccentric weightW to the output shaft S has disadvantages. That is, when an apparatussuch as a pager is designed, a space for rotation of the eccentricweight W should be considered. Also, since an expensive tungsten alloyis used, the manufacturing cost increases.

[0006] Recently, there is a need for a small cylindrical DC motor and amotor having a diameter of 4 mm is being used. However, although a mainbody of a motor has a diameter of 4 mm, the diameter of a space forrotation of the eccentric weight provided at the output shaft should beat least 6 mm to obtain a sufficient amount of vibration. Also, sincethe cylindrical motor cannot be mounted in a mobile phone as it is, anadditional installation member is usually needed. Thus, the cylindricalmotor requires a large space, which makes it difficult to manufacture amobile apparatus which is thin.

[0007] Furthermore, while a great deal of current is consumed, itsefficiency is a mere 20-30%. Accordingly, a flat type motor which cansecure a thickness less than 3 mm is being widely noted.

[0008] The subject applicant has suggested a flat type coreless vibratormotor in Japanese Patent No. 2,137,724 and U.S. Pat. No. 5,036,239. Inthe flat type coreless vibrator motor, an output shaft protrudingoutside the motor is removed and one of three air-core coilssymmetrically arranged on a rotary commutator member is installed at theopposite side of the commutator member, so that the three air-core coilsare grouped together and eccentricity is achieved by inclining the rotoritself.

[0009] Since an effective conductive body of an armature coil of theabove motor is long, a relatively high efficiency can be obtained. Themotor is designed such that a current of about 10 mA flows at a voltageof 3 V. Also, since the output shaft and the eccentric weight do notprotrude outside the motor, there is no great limit in space. However,since three wound type air-core coils are provided at one surface of thecommutator member, the size of the air-core coils needs to be reduced.Thus, the number of parts and steps increases.

[0010] In the above flat type motor having a built-in type eccentricrotor where three armature coils are grouped together, as the motorbecomes smaller, the interval between the armature coils decreases sothat connecting the end portions of the armature coils to the commutatorwith no damage to the armature coils is very difficult. Also, since eachof the armature coils needs to fit within an angle between the adjacentmagnetic poles of a magnet, improvement of efficiency is furtherrequired. Also, since there are three wound type air-core coils, thenumber of parts increases.

[0011] Recently, as mobile phones become smaller, a great amount ofvibration as a silent call means is not needed any more.

SUMMARY OF THE INVENTION

[0012] To solve the above-described problems, it is a first object ofthe present invention to provide a disc type eccentric rotor whichappropriately generates vibrations by means of a centrifugal force withhigh efficiency and can be easily installed, and a flat type vibratormotor using the same.

[0013] It is a second object of the present invention to provide a disctype eccentric rotor which does not need an eccentric member byarranging the center of gravity of the rotor to be eccentric by usingthe coils themselves.

[0014] It is a third object of the present invention to provide a flattype vibrator motor which uses the above flat, disc type eccentric rotorso that high efficiency is achieved, the number of parts is reduced, andmanufacturing cost is lowered.

[0015] It is a fourth object of the present invention to obtainvibrations by using a difference in centrifugal forces, which isachieved by arranging a metal member having a high specific gravity at aportion where no wound type air-core coils exist.

[0016] To achieve the above objects, as disclosed in claim 1, a firstdisc type eccentric rotor having two or more air-core coils andgenerating a difference in centrifugal forces by the rotation of therotor itself, is provided, the rotor comprising a flat type commutatormember having a shaft insertion through hole in the center thereof, aplurality of commutator land segments formed around the shaft insertionthrough hole on a first side of the flat type commutator member, woundtype air-core coil arrangement guides formed outside the shaft insertionthrough hole on a second side of the flat type commutator member,air-core coil end portion connection lands formed circumferentially onthe second side of the flat type commutator member, a shaft holderinstalled around the shaft insertion through hole on the second side ofthe flat type commutator member, and wound type air-core coils installedat the wound type air-core coil arrangement guides and having the endportions thereof connected to the air-core coil end portion connectionlands.

[0017] In the above rotor, as disclosed in claim 2, the air-core coilsare radially arranged at a predetermined angle and at least one air-corecoil is formed as a printed wiring type air-core coil.

[0018] Further, as disclosed in claim 3, the air-core coils comprise oneprinted wiring type air-core coil and two wound type air-core coils, andthe air-core coils are arranged so as not to overlap one another.Otherwise, as disclosed in claim 4, the air-core coils comprise twoprinted wiring type air-core coils and one wound type air-core coil, andthe air-core coils are arranged so as not to overlap one another.

[0019] As disclosed in claim 5, it is preferable that the wound typeair-core coil arrangement guide apertures and reinforcement holes areformed on the printed wiring type commutator member, and thereinforcement holes and the wound type air-core coil arrangement guideapertures are respectively connected through grooves.

[0020] Moreover, as disclosed in claim 6, it is preferable that theshaft holder and the wound type air-core coil arrangement guides areintegrally formed of the same resin by outsert molding on the flat typecommutator member.

[0021] As another way to achieve the above objects, as disclosed inclaim 7, a second disc type eccentric rotor having one or more woundtype air-core coils and generating a difference in centrifugal forces bythe rotation of the rotor itself, is provided, the rotor comprising aflat type commutator member having a shaft insertion through hole in thecenter thereof, a plurality of commutator land segments formed aroundthe shaft insertion through hole on a first side of the flat typecommutator member, a shaft holder installed around the shaft insertionthrough hole on a second side of the flat type commutator member, woundtype air-core coil end portion connection lands formed circumferentiallyon the second side of the flat type commutator member, at least onewound type air-core coil installed outside the shaft holder on thesecond side of the flat type commutator member and having the endportions thereof connected to the wound type air-core coil end portionconnection lands, and an eccentric weight formed of tungsten alloy to beinstalled within the thickness of the wound type air-core coil on thesecond side of the flat type commutator member, the weight fixed to theflat type commutator member by means of resin.

[0022] Further, as disclosed in claim 8, in the second disk typeeccentric rotor, at least one printed wiring type coil is formed at aposition of the flat type commutator member where the eccentric weightis installed.

[0023] As yet another way to achieve the above objects, as disclosed inclaim 9, there is provided a flat type vibrator motor having theeccentric rotor as described above. Here, the flat type vibrator motorcomprises a disc type eccentric rotor having at least one air-core coiland generating a difference in centrifugal forces by the rotation of therotor itself, a shaft for supporting the eccentric rotor, a magnet forproviding a magnetic field for the rotor via a gap therebetween in anaxial direction, a brush arranged inside the magnet for providingelectric power to the air-core coil through the flat type commutatormember, and a housing accommodating all the above elements.

[0024] In the above flat type vibrator motor, as disclosed in claim 10,the shaft is fixed at one side of the housing and a member forpreventing the eccentric rotor from moving in a radial direction isinstalled at the other side of the housing.

[0025] With reference to claim 1, since the rotor is of a disc type, thesize of each air-core coil can be set such that the effective conductiveportions can be positioned within an open angle of two adjacent magneticpoles. Therefore, the maximum vibrations are generated so as to securehigh efficiency. The open angle of two adjacent magnetic poles arecalled “standard electric open angle.” The connection of the coil endportions can be easily performed. Also, the rotor of a disc type can beformed to be eccentric.

[0026] With reference to claim 2, the rotor is not arranged to beinclined toward the side. The size of each air-core coil can be set suchthat the effective conductive portions can be positioned within thestandard electric open angle. Also, since the eccentricity due to thedifference in weight between the printed wiring type air-core coil andthe wound type air-core coil can be anticipated, a disc type rotor whichcan easily generate vibrations by means of the difference in thecentrifugal forces during rotation is possible.

[0027] With reference to claims 3 and 4, since the eccentricity due tothe difference in weight between the printed wiring type air-core coiland the wound type air-core coil can be anticipated, a disc type rotorwhich can easily generate vibrations by means of a difference in thecentrifugal forces during rotation is possible. Also, since one or twowound type air-core coils suffice, the manufacturing cost can bereduced.

[0028] With reference to claim 5, when the shaft holder and the woundtype air-core coil arrangement guides are erected by outsert molding onthe wound type air-core coil arrangement guide apertures and thereinforcement holes, resin fills the insertion pass portion so that thewound type air-core coil arrangement guides, the stop walls, and theshaft holder are integrally connected, which improves strength thereof.

[0029] With reference to claim 6, the shaft holder and the wound typeair-core coil arrangement guides can be formed at once.

[0030] With reference to claims 7 and 8, a disc type rotor can generategreat vibrations due to high specific gravity of tungsten alloy. Sincefewer air-core coils are required, the manufacturing cost is reduced.

[0031] With reference to claims 9 and 10, since the vibrator motor hasthe above-described rotor, the manufacturing cost is reduced while agreat amount of vibrations can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above objects and advantages of the present invention willbecome more apparent by describing in detail preferred embodimentsthereof with reference to the attached drawings in which:

[0033]FIG. 1 is a view showing one side of a flat type commutator memberof a disc type eccentric rotor according to a first preferred embodimentof the present invention;

[0034]FIG. 2 is a view showing the other side of the flat typecommutator member of FIG. 1;

[0035]FIG. 3 is a sectional view of the flat type commutator member,taken along line A-A of FIG.2;

[0036]FIG. 4 is a plan view of a flat type commutator member of a disctype eccentric rotor according to a second preferred embodiment of thepresent invention;

[0037]FIG. 5 is a sectional view showing major portions of a flat typecommutator member of a disc type eccentric rotor according to a thirdpreferred embodiment of the present invention;

[0038]FIG. 6 is a plan view showing a modification example of the rotorof FIG. 5;

[0039]FIG. 7 is a sectional view of a flat type coreless vibrator motorusing the disc type eccentric rotor of FIGS. 2 and 3; and

[0040]FIG. 8 is a perspective view of a conventional small vibratormotor.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Referring to FIG. 1, reference numeral 1 denotes a flat, disctype commutator member as a printed wiring board, at both sides of whicha thin copper plate having a thickness of 0.3 mm is formed. A shaftinsertion hole 1 a is formed at the center of the flat type commutatormember 1. Segments around the shaft insertion hole 1 a which face oneanother are short-circuited by through holes S1 and S2 by using theopposite side of the commutator member so that six commutator landsegments a, b, C, d, e, and f are formed. A printed wiring type air-corecoil 1 b is formed outside the commutator land segments such thateffective conductive portions of the printed wiring type air-core coil,i.e., the portions of the coil which are oriented in the radialdirection and provide the maximum attractive and repulsive forces, arewidened to an angle of about 90° (the same as an angle between twoadjacent magnetic poles with respect to the center of the rotor).

[0042] As shown in FIG. 2, an end portion connection land 1 d and startportion connection lands 1 e and 1 f of the air-core coils 1 b areformed at the outer circumferential portion of the opposite surface ofthe commutator member 1. Here, the start portion of the printed wiringtype air-core coil 1 b is directly connected to the commutator landsegment d of FIG. 1. Partition walls, in which land leads are installed,are formed at positions respectively 120° apart from the centroid of theprinted wiring type air-core coil 1 b. Wound type air-core coilarrangement guide apertures 1 g are arranged at both sides of each ofthe partition walls. Three reinforced holes 1 j formed by punching atpositions which are found symmetrically on a circular arc excluding theprinted wiring type air-core coil 1 b, are connected to the wound typeair-core coil arrangement guide apertures 1 g by an insertion passportion 1 h for reinforcement thereof. The through hole S1 is formed tohave a slightly greater diameter so as to function as a reinforcementhole.

[0043] Also, the printed wiring type air-core coil 1 b is connected inserial to one identically formed at the other side thereof through athrough hole S3 to increase the number of windings. Also, in FIGS. 1 and2, the printed wiring type air-core coil 1 b is represented by solidlines for the convenience of explanation. Since the corners of a printedwiring type air-core coil can be formed to have more acute angles thanthose of a wound type air-core coil, a great torque can be obtained byfully straightening the effective conductive lengths, so that the anglebetween the lengths makes the same angle as that between the twoadjacent magnetic poles.

[0044] Notches g, h, and j are formed at each connection land installedat the outer circumferential portion of the flat commutator member. Whenthe portion of a coil is soldered or heat welded, the coil end portionis held by being hooked at the notches so that the coil can betemporarily fixed.

[0045] Also, the surfaces of the six commutator land segments aregold-plated so that the land segments themselves can form commutatorpieces. Therefore, a flat type commutator can be achieved. Otherwise, ifthe land segments are realized with thin copper plates, a separatecommutator may be connected to the land segments.

[0046] In order to form a disc type eccentric rotor R of FIG. 7 by usingthe above flat type commutator member 1, as shown in FIGS. 2 and 3, ashaft holder 2, two wound type air-core coil arrangement guides 3 andthree stop walls 4 are formed of highly slippery resin having a specificgravity of about 4 at the other surface of the commutator member. Here,the wound type air-core coil arrangement guides 3 function as innersupports inside the coils, and the stop walls 4 also function as outersupports outside the coils. Since the reinforcement hole 1 j and thewound type air-core coil arrangement guide apertures 1 g are connectedto each other via the insertion pass portion 1 h, the wound typeair-core coil arrangement guides 3 and the stop walls 4 are formed onthe reinforcement holes 1 j and the wound type air-core coil arrangementguide apertures 1 g by means of outsert integral molding while themolding resin fills the insertion pass portion 1 h. The wound typeair-core coils 5 formed such that the effective conductive portionsthereof are widened to an angle of about 90°, are installed at the twowound type air-core coil arrangement guides 3.

[0047] The end portions 5 a of the wound type air-core coils 5 areconnected to the end portion connection lands 1 d, 1 e, and 1 f by meansof soldering or heat welding.

[0048]FIG. 4 shows a disc type flat commutator member 11 of a disc typeeccentric rotor according to a second preferred embodiment of thepresent invention. The disc type flat commutator member 11 is formedsuch that two printed wiring type air-core coils 1 b and a wound typeair-core coil 5 can be arranged thereon. In this case, two stop walls 4suffice because they are needed only to determine the position of thewound type air-core coil 5. Also, two end portion connection landsarranged at the outer circumferential portion of the commutator membersuffice. Thus, since only one wound type air-core coil is needed, themanufacturing cost is lowered. In the drawings, the same members havethe same reference numerals and descriptions thereof will be omitted.

[0049]FIG. 5 shows a disc type eccentric rotor having a flat typecommutator member according to a third preferred embodiment of thepresent invention. That is, considering the difference in thicknessbetween the printed wiring type air-core coil 1 b and the wound typeair-core coil 5, to obtain a great amount of vibration, an eccentricweight 66 having a high specific gravity and formed of tungsten alloy isinstalled at the position of a printed wiring type air-core coil 1 b,while the thickness of the eccentric weight 66 is not greater than thatof the wound type air-core coil 5, thus forming an eccentric rotor R1.Thus, even if the eccentric weight 66 is installed, the thickness of theeccentric rotor R1 is not affected.

[0050] In this case, the position of the center of gravity is determinedcontrary to those of the above preferred embodiments. A shaft holder 22,two wound type air-core coil arrangement guides 33, and three stop walls44 are preferably formed of highly slippery resin which is light (forexample, polyamide based resin including potassium titanate whiskerhaving a specific gravity of about 1.3). In other portions of thestructure of the above rotor, the same members have the same referencenumerals and descriptions thereof will be omitted.

[0051]FIG. 6 shows a modification example of the rotor of the thirdpreferred embodiment. The two wound type air-core coils 5 are arrangedat an angle of 110-135° (120° in FIG. 6). The eccentric weight 66 formedof tungsten alloy is placed at the opposite side with respect to a shaftwithin a thickness of the wound type air-core coil 5. The eccentricweight 66 may be integrally fixed to the flat type commutator member 1by means of resin. In this case, the printed wiring type air-core coilis not formed on the side of the commutator member on which theeccentric weight 66 is placed.

[0052] Since the specific weight of the tungsten alloy is 18 or morewhile that of a copper wire of the wound type air-core coil 5 is 8, thecenter of gravity moves toward the eccentric weight 66 so that greateccentricity can be obtained.

[0053]FIG. 7 shows a shaft-fixed flat type vibrator motor having theeccentric rotor shown in FIGS. 2 and 3. That is, the motor includes aneccentric rotor R, a shaft 7 for supporting the eccentric rotor R to becapable of rotating, a magnet 8 for applying a magnetic field to theeccentric rotor R via a gap therebetween, a brush 9 arranged inside themagnet 8 for applying electric power to each of the printed wiring typeand wound type air-core coils 1 b and 5 via the flat type commutatormember 1, and a housing 10 including a case 10 a for accommodating allthe above-mentioned members and a bracket 10 b for fixing the shaft 7.

[0054] In FIG. 7, reference letter P denotes a sliding member formed ofa polyester film. When the eccentric rotor R is elastically pressedtoward the case 10 a by a pressing force of the brush 9, the slidingmember P slides smoothly. Also, the sliding member P prevents the shaft7 from protruding outside the case 10 a. The sliding member P restrictsthe movement of the shaft 7 in a radial direction so as to be resistantto impacts such as dropping. In FIG. 7, reference letter F denotes aflexible electricity feeding lead wire to which the brush 9 is soldered.

[0055] In each of the above-preferred embodiments, the printed wiringtype air-core coils are formed at both sides of the flat type commutatormember 1 in two layers. However, the number of windings can be increasedby forming a 4-6 layered printed wiring type air-core coil by arranginga multilayer substrate having two or three laminated printed wiringboards each having a thickness of about 0.1 mm at both sides of the flattype commutator member 1.

[0056] Also, in each of the above-preferred embodiments, the wound typeair-core coil is placed on a printed wiring board. However, part of thewound type air-core coil may be buried by forming the wound typeair-core coil arrangement guide aperture to be slightly greater than thewound type air-core coil in the printed wiring board. Otherwise, thewound type air-core coil may be entirely covered with the slipperyresin. Thus, the gap between the magnet and the wound type air-core coilcan be reduced by the thickness of the printed wiring board, so that theair-gap magnetic flux density can increase substantially.

[0057] Also, although the shaft holder formed of resin functions as abearing, a metal sintered oily bearing may be used as the shaft holder.Further, it is possible that the shaft is fixed to the eccentric rotorand a bearing is arranged at the housing.

[0058] As described above, in the disc type eccentric rotor having theabove structure according to the present invention, vibrations due to acentrifugal force are appropriately generated and the air-core coils areformed to be great and uniformly arranged, so that high efficiency canbe obtained. Also, since one or two wound type air-core coils suffice,installation and line connection can be easily performed.

[0059] With reference to claim 1, since the flat type commutator memberis a disc type, the size of each air-core coil can be set such that theeffective conductive portions can be positioned within an open angle oftwo adjacent magnetic poles. The connection of the coil end portion canbe easily performed. Also, the rotor of a disc type can be formed to beeccentric.

[0060] With reference to claim 2, the rotor is not arranged to beinclined toward the side. The size of each air-core coil can be set suchthat the effective conductive portions can be positioned within thestandard electric open angle. Also, since the eccentricity due to thedifference in weight between the printed wiring type air-core coil andthe wound type air-core coil can be anticipated, a disc type rotor whichcan easily generate vibrations by means of a centrifugal force duringrotation is possible.

[0061] With reference to claims 3 and 4, since the eccentricity due tothe difference in weight between the printed wiring type air-core coiland the wound type air-core coil can be anticipated, a disc type rotorwhich can easily generate vibrations by means of a centrifugal forceduring rotation is possible. Also, since one or two wound type air-corecoils suffice, the manufacturing cost can be reduced.

[0062] With reference to claim 5, when the shaft holder and the woundtype air-core coil arrangement guides are erected by outsert molding onthe wound type air-core coil arrangement guide apertures and thereinforcement holes, resin fills the insertion pass portion so that thewound type air-core coil arrangement guides, the stop walls, and theshaft holder are integrally connected, which improves strength thereof.

[0063] With reference to claim 6, the shaft holder and the wound typeair-core coil arrangement guides can be formed at once.

[0064] With reference to claims 7 and 8, a disc type rotor generatinggreat vibrations can be obtained due to high specific gravity oftungsten alloy. Since fewer air-core coils are required, themanufacturing cost is reduced.

[0065] With reference to claims 9 and 10, since the vibrator motor hasthe above-described rotor, the manufacturing cost is reduced while agreat amount of vibrations can be obtained.

[0066] While this invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A disc type eccentric rotor having two or moreair-core coils and generating a difference in centrifugal forces by therotation of the rotor itself, the rotor comprising: a flat typecommutator member having a shaft insertion through hole in the centerthereof; a plurality of commutator land segments formed around the shaftinsertion through hole on a first side of the flat type commutatormember; wound type air-core coil arrangement guides formed outside theshaft insertion through hole on a second side of the flat typecommutator member; air-core coil end portion connection lands formedcircumferentially on the second side of the flat type commutator member;a shaft holder installed around the shaft insertion through hole on thesecond side of the flat type commutator member; and wound type air-corecoils installed at the wound type air-core coil arrangement guides andhaving the end portions thereof connected to the air-core coil endportion connection lands.
 2. The rotor as claimed in claim 1, whereinthe air-core coils are radially arranged at a predetermined angle and atleast one air-core coil is formed as a printed wiring type air-corecoil.
 3. The rotor as claimed in claim 2, wherein the air-core coilscomprise one printed wiring type air-core coil and two wound typeair-core coils, and the air-core coils are arranged so as not to overlapone another.
 4. The rotor as claimed in claim 2, wherein the air-corecoils comprise two printed wiring type air-core coils and one wound typeair-core coil, and the air-core coils are arranged so as not to overlapone another.
 5. The rotor as claimed in claim 1, wherein wound typeair-core coil arrangement guide apertures and reinforcement holes areformed on the printed wiring type commutator member, and thereinforcement holes and the wound type air-core coil arrangement guideapertures are respectively connected through grooves.
 6. The rotor asclaimed in claim 4, wherein the shaft holder and the wound type air-corecoil arrangement guides are integrally formed of the same resin byoutsert molding on the flat type commutator member.
 7. A disc typeeccentric rotor having one or more wound type air-core coils andgenerating a difference in centrifugal forces by the rotation of therotor itself, the rotor comprising: a flat type commutator member havinga shaft insertion through hole in the center thereof; a plurality ofcommutator land segments formed around the shaft insertion through holeon a first side of the flat type commutator member; a shaft holderinstalled around the shaft insertion through hole on a second side ofthe flat type commutator member; wound type air-core coil end portionconnection lands formed circumferentially on the second side of the flattype commutator member; at least one wound type air-core coil installedoutside the shaft holder on the second side of the flat type commutatormember and having the end portions thereof connected to the wound typeair-core coil end portion connection lands; and an eccentric weightformed of tungsten alloy to be installed within the thickness of thewound type air-core coil on the second side of the flat type commutatormember, the weight fixed to the flat type commutator member by means ofresin.
 8. The rotor as claimed in claim 7, wherein at least one printedwiring type coil is formed at a position of the flat type commutatormember where the eccentric weight is installed.
 9. A flat type vibratormotor comprising: a disc type eccentric rotor having at least oneair-core coil and generating a difference in centrifugal forces by therotation of the rotor itself; a shaft for supporting the eccentricrotor; a magnet for providing a magnetic field for the rotor via a gaptherebetween in an axial direction; a brush arranged inside the magnetfor providing electric power to the air-core coil through the flat typecommutator member, and a housing accommodating all the above elements.10. The vibrator motor as claimed in claim 9, wherein the shaft is fixedat one side of the housing and a member for preventing the eccentricrotor from moving in a radial direction is installed at the other sideof the housing.